ima: accept previously set IMA_NEW_FILE

commit 1ac202e9 upstream.

Modifying the attributes of a file makes ima_inode_post_setattr reset
the IMA cache flags. So if the file, which has just been created,
is opened a second time before the first file descriptor is closed,
verification fails since the security.ima xattr has not been written
yet. We therefore have to look at the IMA_NEW_FILE even if the file
already existed.

With this patch there should no longer be an error when cat tries to
open testfile:

$ rm -f testfile
$ ( echo test >&3 ; touch testfile ; cat testfile ) 3>testfile

A file being new is no reason to accept that it is missing a digital
signature demanded by the policy.
Signed-off-by: Daniel Glöckner <dg@emlix.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

security/integrity/ima/ima_appraise.c

@@ -195,10 +195,11 @@ int ima_appraise_measurement(int func, struct integrity_iint_cache *iint,
 
 		cause = "missing-hash";
 		status = INTEGRITY_NOLABEL;
-		if (opened & FILE_CREATED) {
+		if (opened & FILE_CREATED)
 			iint->flags |= IMA_NEW_FILE;
+		if ((iint->flags & IMA_NEW_FILE) &&
+		    !(iint->flags & IMA_DIGSIG_REQUIRED))
 			status = INTEGRITY_PASS;
-		}
 		goto out;
 	}